Preheat the oven to 200°C/400°F/gas mark 6. Line a 30 × 40 cm (12 × 16 in.) baking sheet with lightly oiled parchment paper to prevent the pancake from sticking to the tray as it cooks.
To make the batter
Put the ripe bananas in a medium mixing bowl and mash well using a fork. Stir in the milk, vinegar, olive oil and vanilla extract. In a separate larger mixing bowl, combine the flour, baking powder, sea salt and cinnamon. Form a well in the middle of the dry ingredients, and then, mixing constantly (to ensure a smooth batter), gradually pour the wet ingredients into the dry mixture. Whisk together well.
Pour the pancake batter into the prepared baking sheet and smooth evenly to the edges.
To make the topping
Scatter the blueberries over the batter and sprinkle the sugar evenly over the top. Bake for 30 minutes until golden brown and springy to the touch. Leave to rest for a couple of minutes for ease of cutting.
Cut into 12 rectangles and plate 3 pieces per person, drizzle with maple syrup, place berries on the side and add a swirl of cream (if using).